1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copying machine, a facsimile or a printer, which forms an image using electrophotography, and to a mixed toner discharge control method.
2. Description of the Related Art
Jpn. Pat. Appln. KOKAI Publication No. 2001-188394 discloses a technique relating to cleaning of toner in a developing device in a color image forming apparatus, in a case where toner of a previously developed toner image is reversely transferred and mixed in the developing device that subsequently develops a toner image.
According to this technique, in an image forming apparatus having a plurality of image forming sections, when an image ratio of an image formed in one of two adjacent image forming sections, which is disposed at a rear stage, is lower than an image ratio of an image formed in the image forming section at a front stage, the image forming section at the rear stage operates to forcibly consume a developer, in addition to toner consumption in an ordinary image forming operation.
This technique, however, has the following problem.
For example, in an image forming apparatus that performs image formation using four color toners, assume that image forming sections, the number of which is equal to the number of colors, i.e. four, are provided. In this technique, only the operation of the image forming section, which has performed an image forming operation immediately before, is monitored. Thus, no consideration is given to mixing of toner in image forming sections that form third and fourth toner images, relative to the image forming section that forms a first toner image. As a result, even if toning of color tone of toner images formed in the third and fourth image forming sections has varied, forcible discharge of developer is not performed.